Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
As is known in the art, positioning technologies generally operate by measuring the time a signal takes to traverse from a signal source to the receiving device. In most prior art applications, this measurement is taken by comparing the time at which a signal is sent with the time at which the same signal is received. Common positioning systems such as GPS use three or more such signals and, using trilateration, calculate an object's position. Since the measurement calculations are time-sensitive, a fourth signal is commonly required to ensure that the clocks of the source and the receiver are properly synchronised.
Multipath refers to the phenomenon whereby positioning signals are reflected off other objects, such as walls and furniture. This is especially prevalent in an enclosed environment, such as indoors, but is also a significant problem in built up areas, such as in cities. Simplistically speaking, reflected signals take longer to traverse from a source to a receiver, therefore affecting the accuracy of the measurements. Also the receiver sees conflicting signals originating from the same source, having different timing information. Some modern receivers use selection algorithms to try to determine the most appropriate signal to use in position determination. However, receivers typically cannot differentiate multipath signals from the genuine positioning signals to any high degree of accuracy.
Also known in the art are phased arrays, consisting of a number of antenna elements that can be individually controlled to direct a beam. In a typical phased array, signals received at each element are individually phase and gain manipulated, the exact manipulation required depending on the direction of the beam required. The resulting phase and gain manipulated signals from each element are then summed to obtain the desired direction of the beam.
One method for mitigating the problem of multipath is discussed in published international patent application WO 2011/000049 A1 which is assigned to the present applicant and hereby incorporated in its entirety by reference. This application discusses a method to form a beam using a local receiver antenna to receive a positioning signal from a transmission source, thereby ignoring other signals in a multipath environment.
While this method is successful in mitigating the effects of multipath, the local receiver antenna necessarily requires a number of physical antenna elements. This limits the size to which the local receiver antenna can be miniaturised, and therefore limits the portability of the receiver. Portability is not an issue when the receiving apparatus is to be mounted to, for example, a forklift. However, if receiving apparatus is to be incorporated into, for example, a mobile telephone, then further miniaturisation of the receiver antenna is necessary.
The present invention describes an apparatus and method for utilising antenna technology that is already deployed in portable hand-held equipment in high-precision positioning applications.